CHAPTER 6: Sustaining Hydrogen Production in Eukaryotic Microalgae Through Genetic Approaches

The efficiency of H₂ production with microalgae is generally hampered by the fact that under in vivo conditions the bio-catalytic conversion of protons and electrons to hydrogen is only used as a limited valve system, reacting to severe stress conditions to prevent cell damage caused by an imbalance of the cellular redox-homeostasis. The participating hydrogenase enzyme in eukaryotic microalgae has a large enzymatic capacity; however, high H₂-production rates are mainly prevented by insufficient delivery of protons and electrons. To overcome this bottleneck, molecular engineering of specific parts of the cellular metabolism has been considered as a promising approach. Recent achievements using forward and reverse genetic approaches for the identification and construction of efficient, eukaryotic-microalgal H₂ producers resulted in the isolation of high H₂ producers with production rates up to 850 ml H₂ l⁻¹ cell culture. Application strategies include systematic genomics to identify and isolate new, high H₂, GMO-cell lines through different screening programs from libraries constructed by random mutagenesis, as well as targeted mutagenesis approaches combined with systems biology required for the localization of potential bottlenecks.